Easiest way from Gatwick Airport to Bath Spa?

Hello all, I would like to get to Bath Spa from GTW, what do you think is the easiest way to get there? And not necessarily the most expensive way, but then again, I am travelling with a 2 y.o. toddler, so I am willing to pay more for a smooth trip. I was looking for information online. I was planning to travel from the airport to Reading Station, change trains there and go to Bath. But tripadvisor suggested me to rather go to Heathrow bus station first, and take the National Express Coach directly to Bath Spa. As I looked this would cost me a little bit more. Which way would you suggest?

Also I will have some extra Euros with me, can I go to a bank or post office in Bath to exchange currency, or do I need to find a currency exchange place? Thank you for your help!!